This invention relates to a method of storing natural gas. More particularly, the invention relates to storage of natural gas at near ambient temperatures using a solid adsorbent, in particular, a carbon molecular sieve.
In U.S. Pat. No. 4,820,681 two of the present inventors have disclosed an improved carbon molecular sieve which has a high capacity for carbon dioxide and may be characterized as hydrophobic, requires no binders, and may be carbonized in a single step.
Natural gas, being substantially methane, has a low molecular weight and it occupies a large volume per unit weight compared to liquid fuels. Thus, reducing the volume of natural gas is necessary for most practical applications of natural gas as a fuel. Methods for doing this could include (1) storage at high pressure, (2) liquefaction and storage at low temperatures, and (3) adsorption on solids. Of these methods the last is of particular interest since compact storage of natural gas at moderate pressures may be achieved, while avoiding the cryogenic temperatures needed for liquid natural gas or the high pressures needed for storage as a gas in reasonable volumes.
Conventional activated carbons have been found to have reasonable capacity for natural gas but higher capacity is believed necessary for commercial success. Inorganic zeolites have also been tried, but found to have relatively low capacity for natural gas. Carbon molecular sieves also have been suggested for adsorption of natural gas. The present inventors have sought improvements in the storage of natural gas and have found the materials and methods to be disclosed below.